Issued by NWS Denver/Boulder, CO
000
UXUS97 KBOU 061228
SRGBOU
Soaring Forecast
National Weather Service Denver/Boulder, Colorado
628 AM MDT Wednesday May 6, 2009
This forecast is for Wednesday May 6, 2009:
If the trigger temperature of 65.2 F/18.5 C is reached...then
Thermal Soaring Index....................... Excellent
Maximum rate of lift........................ 991 ft/min (5.0 m/s)
Maximum height of thermals.................. 16883 ft MSL (11598 ft AGL)
Forecast maximum temperature................... 78.0 F/26.0 C
Time of trigger temperature.................... 1015 MDT
Time of overdevelopment........................ None
Middle/high clouds during soaring window....... None
Surface winds during soaring window............ 20 mph or less
Height of the -3 thermal index................. 15512 ft MSL (10227 ft AGL)
Thermal soaring outlook for Thursday 05/07..... Excellent
Wave Soaring Index............................. Good
Wave Soaring Index trend (to 1800 MDT)......... Little change
Height of stable layer (12-18K ft MSL)......... 16126 ft MSL (10841 ft AGL)
Weak PVA/NVA (through 1800 MDT)................ Weak NVA
Potential height of wave....................... 43967 ft MSL (38682 ft AGL)
Wave soaring outlook for Thursday 05/07........ Fair
Remarks...
Sunrise/Sunset.................... 05:53:55 / 19:58:01 MDT
Total possible sunshine........... 14 hr 4 min 7 sec (844 min 7 sec)
Altitude of sun at 12:56:09 MDT... 66.95 degrees
Upper air data from rawinsonde observation taken on 05/06/2009 at 0600 MDT
Freezing level.................. 11603 ft MSL (6318 ft AGL)
Convective condensation level... 14923 ft MSL (9638 ft AGL)
Lifted condensation level....... 16787 ft MSL (11502 ft AGL)
Lifted index.................... -0.1
K index......................... +5.7
Height Temperature Wind Wind Spd Lapse Rate ConvectionT Thermal Lift Rate
ft MSL deg C deg F Dir kt m/s C/km F/kft deg C deg F Index fpm m/s
--------------------------------------------------------------------------------
50000 -65.2 -85.4 305 79 41 -8.5 -4.6 89.0 192.2 36.4 M M
45000 -64.7 -84.5 310 114 59 5.0 2.8 64.8 148.6 24.2 M M
40000 -58.6 -73.5 310 113 58 8.2 4.5 51.4 124.5 17.1 M M
38000 -53.8 -64.8 312 110 56 7.9 4.3 49.5 121.1 16.3 M M
36000 -49.1 -56.4 314 107 55 6.8 3.7 48.1 118.6 15.7 M M
34000 -47.2 -53.0 306 99 51 8.5 4.6 42.3 108.2 12.0 M M
32000 -41.5 -42.7 312 89 46 8.4 4.6 41.0 105.8 11.4 M M
30000 -36.9 -34.4 314 83 43 6.0 3.3 39.6 103.3 10.6 M M
29000 -35.0 -31.0 314 80 41 6.1 3.3 38.1 100.6 9.6 M M
28000 -33.1 -27.6 313 77 40 7.8 4.3 36.9 98.4 8.7 M M
27000 -30.8 -23.4 312 74 38 7.6 4.2 36.0 96.9 8.2 M M
26000 -28.5 -19.3 311 72 37 8.2 4.5 35.3 95.6 7.7 M M
25000 -26.4 -15.5 310 69 36 7.7 4.2 34.3 93.7 7.0 M M
24000 -24.4 -11.9 308 64 33 4.5 2.5 33.1 91.5 6.1 M M
23000 -22.7 -8.9 300 57 29 8.7 4.8 31.6 88.8 5.0 M M
22000 -20.2 -4.4 300 58 30 8.5 4.7 31.0 87.9 4.6 M M
21000 -17.6 0.3 300 59 30 8.5 4.7 30.6 87.1 4.3 M M
20000 -15.2 4.6 300 60 31 3.6 2.0 30.0 86.0 3.8 M M
19500 -15.0 5.0 300 58 30 2.8 1.5 28.6 83.5 2.6 M M
19000 -14.1 6.6 300 56 29 7.8 4.3 27.9 82.3 2.1 M M
18500 -13.0 8.6 299 54 28 6.7 3.7 27.5 81.5 1.7 M M
18000 -12.0 10.4 297 54 28 6.6 3.6 26.9 80.4 1.2 M M
17500 -11.0 12.2 295 53 27 6.6 3.6 26.3 79.4 0.7 M M
17000 -10.1 13.8 294 53 27 6.6 3.6 25.8 78.4 0.2 M M
16500 -9.1 15.6 292 53 27 7.4 4.1 25.3 77.5 -0.2 967 4.9
16000 -8.8 16.2 290 53 27 -0.6 -0.3 23.2 73.8 -2.1 936 4.8
15500 -8.4 16.9 290 52 27 5.4 2.9 22.1 71.8 -3.2 909 4.6
15000 -7.8 18.0 290 52 27 4.0 2.2 21.3 70.3 -4.1 876 4.4
14500 -7.1 19.2 290 51 26 7.1 3.9 20.4 68.7 -5.0 843 4.3
14000 -5.8 21.6 289 51 26 8.6 4.7 20.2 68.4 -5.1 789 4.0
13500 -4.5 23.9 287 52 27 8.2 4.5 20.1 68.1 -5.3 735 3.7
13000 -3.5 25.7 285 51 26 8.1 4.5 19.7 67.5 -5.8 688 3.5
12500 -2.2 28.0 287 45 23 8.4 4.6 19.5 67.1 -6.0 637 3.2
12000 -0.9 30.4 290 39 20 9.2 5.1 19.4 66.8 -6.2 582 3.0
11500 0.4 32.7 290 35 18 9.2 5.0 19.2 66.6 -6.4 527 2.7
11000 1.8 35.2 290 31 16 9.2 5.0 19.1 66.4 -6.5 471 2.4
10500 3.2 37.8 290 27 14 9.1 5.0 19.0 66.3 -6.6 415 2.1
10250 3.9 39.0 290 25 13 9.3 5.1 19.0 66.2 -6.7 387 2.0
10000 4.6 40.3 290 24 12 9.6 5.3 19.0 66.2 -6.7 359 1.8
9750 5.3 41.5 293 23 12 9.7 5.3 19.0 66.2 -6.7 330 1.7
9500 6.0 42.8 295 22 11 9.7 5.3 19.0 66.2 -6.8 301 1.5
9250 6.7 44.1 297 22 11 9.7 5.3 19.0 66.2 -6.8 272 1.4
9000 7.4 45.3 300 21 11 9.5 5.2 19.0 66.2 -6.8 243 1.2
8750 8.2 46.8 302 20 11 10.3 5.7 19.0 66.2 -6.9 214 1.1
8500 8.9 48.0 304 20 10 7.3 4.0 19.0 66.2 -6.9 185 0.9
8250 9.2 48.6 307 19 10 3.5 1.9 18.6 65.4 -7.3 168 0.9
8000 9.4 48.9 310 19 10 3.6 2.0 18.1 64.6 -7.8 154 0.8
7750 9.6 49.3 312 16 8 4.0 2.2 17.6 63.7 -8.4 140 0.7
7500 10.0 50.0 315 13 7 7.5 4.1 17.3 63.1 -8.7 121 0.6
7250 10.7 51.3 320 10 5 9.5 5.2 17.3 63.1 -8.8 94 0.5
7000 11.4 52.5 329 7 4 9.1 5.0 17.2 63.0 -8.9 66 0.3
6750 12.0 53.6 337 5 3 8.8 4.8 17.2 62.9 -9.0 38 0.2
6500 12.7 54.9 353 4 2 10.3 5.7 17.1 62.8 -9.1 11 0.1
6250 13.4 56.1 027 2 1 4.5 2.5 17.1 62.7 -9.1 M M
6000 13.4 56.1 071 3 1 5.0 2.7 16.5 61.7 -9.8 M M
5750 13.2 55.8 091 2 1 -24.0 -13.2 15.6 60.1 -10.9 M M
5500 9.1 48.4 150 1 1 -78.1 -42.8 10.8 51.4 -15.7 89 0.5
* * * * * * Numerical weather prediction model forecast data valid * * * * * *
05/06/2009 at 0900 MDT | 05/06/2009 at 1200 MDT
|
K index... +3.4 | K index... +10.8
|
Height Temperature Wnd WndSpd Lapse Rate | Temperature Wnd WndSpd Lapse Rate
ft MSL deg C deg F Dir kt m/s C/km F/kft | deg C deg F Dir kt m/s C/km F/kft
--------------------------------------------------------------------------------
50000 -63.0 -81.4 309 68 35 -1.0 -0.6 | -63.1 -81.6 304 61 32 -0.1 -0.0
45000 -63.3 -81.9 309 101 52 5.3 2.9 | -62.1 -79.8 305 89 46 4.8 2.6
40000 -55.4 -67.7 311 103 53 5.2 2.8 | -54.9 -66.8 307 97 50 4.7 2.6
38000 -51.9 -61.4 311 98 51 5.8 3.2 | -51.5 -60.7 306 90 46 5.7 3.2
36000 -48.4 -55.1 311 92 47 5.8 3.2 | -48.1 -54.6 305 81 42 5.7 3.2
34000 -44.8 -48.6 310 85 44 6.2 3.4 | -43.8 -46.8 301 75 39 6.8 3.7
32000 -41.1 -42.0 307 77 40 6.2 3.4 | -39.7 -39.5 297 72 37 6.8 3.8
30000 -36.7 -34.1 306 71 37 7.1 3.9 | -35.7 -32.3 293 68 35 6.9 3.8
29000 -34.5 -30.1 306 70 36 7.1 3.9 | -33.6 -28.5 291 66 34 6.9 3.8
28000 -32.4 -26.3 306 68 35 7.1 3.9 | -31.5 -24.7 289 64 33 6.9 3.8
27000 -30.2 -22.4 305 66 34 8.0 4.4 | -29.3 -20.7 288 63 33 8.1 4.4
26000 -27.8 -18.0 305 65 33 8.0 4.4 | -26.9 -16.4 288 62 32 8.1 4.5
25000 -25.4 -13.7 305 63 32 8.0 4.4 | -24.5 -12.1 288 62 32 8.1 4.5
24000 -23.2 -9.8 305 60 31 6.0 3.3 | -22.1 -7.8 288 60 31 7.5 4.1
23000 -21.3 -6.3 305 56 29 6.2 3.4 | -19.8 -3.6 288 56 29 7.6 4.2
22000 -19.5 -3.1 305 51 26 6.2 3.4 | -17.6 0.3 288 52 27 7.6 4.1
21000 -17.6 0.3 304 47 24 5.6 3.1 | -15.4 4.3 288 50 25 6.4 3.5
20000 -16.0 3.2 303 46 24 5.7 3.1 | -13.5 7.7 286 48 25 6.4 3.5
19500 -15.1 4.8 303 45 23 5.7 3.1 | -12.5 9.5 285 47 24 6.4 3.5
19000 -14.3 6.3 302 44 23 5.6 3.1 | -11.6 11.1 284 47 24 6.7 3.7
18500 -13.4 7.9 302 44 22 5.9 3.2 | -10.4 13.3 284 45 23 4.3 2.4
18000 -12.5 9.5 302 43 22 5.9 3.2 | -9.8 14.4 285 44 23 4.3 2.3
17500 -11.7 10.9 301 42 22 6.1 3.3 | -9.2 15.4 286 42 22 3.8 2.1
17000 -10.3 13.5 302 40 21 6.3 3.5 | -8.6 16.5 286 38 20 3.9 2.1
16500 -9.3 15.3 302 39 20 6.7 3.7 | -8.0 17.6 286 35 18 4.6 2.5
16000 -8.3 17.1 303 38 20 6.9 3.8 | -7.3 18.9 285 32 17 5.0 2.7
15500 -7.3 18.9 304 37 19 7.0 3.8 | -6.6 20.1 285 30 16 5.3 2.9
15000 -6.2 20.8 305 35 18 7.3 4.0 | -5.7 21.7 283 29 15 6.3 3.5
14500 -5.1 22.8 305 33 17 7.3 4.0 | -4.8 23.4 282 28 15 6.3 3.4
14000 -4.0 24.8 306 31 16 8.2 4.5 | -3.8 25.2 279 27 14 8.0 4.4
13500 -2.8 27.0 307 29 15 8.2 4.5 | -2.7 27.1 276 25 13 7.8 4.3
13000 -1.6 29.1 307 28 14 8.0 4.4 | -1.5 29.3 273 24 12 9.2 5.0
12500 -0.5 31.1 306 27 14 7.9 4.4 | -0.1 31.8 270 22 11 9.2 5.0
12000 0.7 33.3 305 26 13 8.4 4.6 | 1.2 34.2 267 20 10 9.2 5.0
11500 2.0 35.6 304 26 14 8.5 4.7 | 2.6 36.7 265 18 9 9.2 5.0
11000 3.2 37.8 303 26 13 8.1 4.5 | 3.9 39.0 263 16 8 9.1 5.0
10500 4.4 39.9 303 25 13 8.1 4.4 | 5.3 41.5 259 15 8 9.1 5.0
10250 5.0 41.0 303 24 12 8.0 4.4 | 5.9 42.6 257 14 7 8.8 4.8
10000 5.6 42.1 302 22 12 7.8 4.3 | 6.6 43.9 255 13 7 8.3 4.6
9750 6.1 43.0 302 21 11 7.8 4.3 | 7.2 45.0 253 12 6 8.2 4.5
9500 6.7 44.1 302 19 10 7.8 4.3 | 7.8 46.0 250 11 6 8.2 4.5
9250 7.3 45.1 302 18 9 7.7 4.2 | 8.4 47.1 247 10 5 8.4 4.6
9000 7.8 46.0 301 17 9 7.5 4.1 | 9.1 48.4 244 9 5 8.6 4.7
8750 8.4 47.1 299 15 8 7.5 4.1 | 9.7 49.5 241 8 4 8.7 4.7
8500 8.9 48.0 297 14 7 7.5 4.1 | 10.4 50.7 237 8 4 8.5 4.7
8250 9.5 49.1 295 13 7 7.3 4.0 | 11.0 51.8 233 7 4 9.2 5.0
8000 10.0 50.0 292 12 6 7.0 3.9 | 11.7 53.1 231 7 3 9.8 5.4
7750 10.5 50.9 287 11 5 7.1 3.9 | 12.4 54.3 228 6 3 9.6 5.3
7500 11.0 51.8 282 10 5 7.2 3.9 | 13.1 55.6 226 6 3 9.7 5.3
7250 11.6 52.9 275 9 4 7.6 4.2 | 13.9 57.0 223 5 3 10.0 5.5
7000 12.1 53.8 268 8 4 7.7 4.2 | 14.6 58.3 223 5 3 10.1 5.5
6750 12.7 54.9 259 7 4 8.1 4.4 | 15.4 59.7 222 5 3 10.0 5.5
6500 13.3 55.9 250 7 4 6.3 3.5 | 16.1 61.0 221 5 2 10.2 5.6
6250 13.6 56.5 242 7 3 4.4 2.4 | 16.9 62.4 221 5 2 10.6 5.8
6000 13.9 57.0 235 6 3 4.2 2.3 | 17.7 63.9 220 4 2 10.1 5.5
5750 14.2 57.6 226 6 3 6.0 3.3 | 18.5 65.3 220 4 2 11.9 6.5
5500 14.8 58.6 222 6 3 13.3 7.3 | 19.6 67.3 222 4 2 20.3 11.1
05/06/2009 at 1500 MDT | 05/06/2009 at 1800 MDT
|
K index... +21.3 | K index... +20.4
|
Height Temperature Wnd WndSpd Lapse Rate | Temperature Wnd WndSpd Lapse Rate
ft MSL deg C deg F Dir kt m/s C/km F/kft | deg C deg F Dir kt m/s C/km F/kft
--------------------------------------------------------------------------------
50000 -64.0 -83.2 296 59 31 1.0 0.6 | -64.5 -84.1 291 65 34 1.5 0.8
45000 -61.6 -78.9 300 85 44 4.9 2.7 | -61.5 -78.7 294 91 47 4.6 2.5
40000 -53.9 -65.0 299 100 51 5.2 2.9 | -54.4 -65.9 293 99 51 5.2 2.9
38000 -50.6 -59.1 299 91 47 5.6 3.1 | -50.8 -59.4 293 93 48 5.9 3.2
36000 -47.3 -53.1 298 83 43 5.6 3.1 | -47.3 -53.1 293 88 45 5.9 3.2
34000 -43.4 -46.1 297 77 39 7.0 3.8 | -43.3 -45.9 294 83 42 7.1 3.9
32000 -39.3 -38.7 296 72 37 7.0 3.8 | -39.1 -38.4 295 78 40 7.1 3.9
30000 -35.4 -31.7 293 67 35 5.9 3.2 | -34.6 -30.3 295 72 37 6.3 3.5
29000 -33.2 -27.8 292 65 33 5.9 3.2 | -32.7 -26.9 294 69 36 6.3 3.5
28000 -31.5 -24.7 290 63 32 5.8 3.2 | -30.8 -23.4 294 66 34 6.4 3.5
27000 -29.5 -21.1 289 60 31 7.2 4.0 | -29.0 -20.2 294 64 33 6.1 3.4
26000 -27.3 -17.1 289 56 29 7.3 4.0 | -27.1 -16.8 294 63 32 6.1 3.4
25000 -25.1 -13.2 289 52 27 7.3 4.0 | -25.3 -13.5 294 61 31 6.2 3.4
24000 -22.9 -9.2 289 51 26 8.3 4.6 | -23.2 -9.8 293 58 30 8.0 4.4
23000 -20.4 -4.7 291 52 27 8.3 4.5 | -20.8 -5.4 291 52 27 8.0 4.4
22000 -17.9 -0.2 293 53 27 8.3 4.5 | -18.4 -1.1 289 46 23 8.0 4.4
21000 -15.6 3.9 294 52 27 7.4 4.1 | -16.1 3.0 288 41 21 7.9 4.3
20000 -13.4 7.9 293 51 26 7.4 4.1 | -13.7 7.3 288 37 19 7.9 4.3
19500 -12.3 9.9 293 50 26 7.4 4.1 | -12.6 9.3 288 35 18 7.9 4.4
19000 -11.2 11.8 292 49 25 7.3 4.0 | -11.4 11.5 288 32 17 7.9 4.3
18500 -10.3 13.5 292 47 24 5.9 3.3 | -10.3 13.5 289 32 17 7.5 4.1
18000 -9.4 15.1 290 45 23 6.1 3.3 | -9.2 15.4 291 33 17 7.6 4.2
17500 -8.5 16.7 289 43 22 5.2 2.9 | -8.1 17.4 292 34 17 6.7 3.7
17000 -7.8 18.0 288 40 21 4.9 2.7 | -7.2 19.0 292 34 18 6.5 3.6
16500 -7.1 19.2 286 38 19 5.0 2.8 | -6.2 20.8 291 34 18 6.5 3.6
16000 -5.9 21.4 283 35 18 5.7 3.1 | -4.8 23.4 290 33 17 6.5 3.6
15500 -5.2 22.6 282 33 17 6.4 3.5 | -3.9 25.0 289 33 17 6.8 3.7
15000 -4.1 24.6 280 30 15 7.4 4.1 | -2.9 26.8 287 30 15 7.2 3.9
14500 -3.0 26.6 278 28 14 7.5 4.1 | -1.9 28.6 285 27 14 7.4 4.1
14000 -1.9 28.6 277 25 13 8.3 4.6 | -0.7 30.7 283 25 13 8.8 4.8
13500 -0.7 30.7 275 22 11 8.2 4.5 | 0.6 33.1 281 23 12 8.6 4.7
13000 0.6 33.1 273 19 10 9.5 5.2 | 1.9 35.4 279 21 11 9.7 5.3
12500 2.0 35.6 272 17 9 9.4 5.1 | 3.3 37.9 278 21 11 9.6 5.3
12000 3.4 38.1 272 15 8 9.3 5.1 | 4.7 40.5 277 20 10 9.4 5.1
11500 4.8 40.6 272 14 7 9.2 5.1 | 6.1 43.0 277 19 10 9.3 5.1
11000 6.2 43.2 273 12 6 9.6 5.3 | 7.5 45.5 277 18 9 9.6 5.3
10500 7.6 45.7 274 11 6 9.6 5.3 | 9.0 48.2 277 18 9 9.6 5.3
10250 8.3 46.9 274 10 5 9.7 5.3 | 9.7 49.5 277 18 9 9.7 5.3
10000 9.0 48.2 274 10 5 9.9 5.4 | 10.4 50.7 278 17 9 9.9 5.4
9750 9.8 49.6 274 10 5 9.9 5.5 | 11.2 52.2 278 17 9 9.9 5.5
9500 10.5 50.9 275 10 5 10.0 5.5 | 11.9 53.4 278 17 9 10.0 5.5
9250 11.3 52.3 275 10 5 9.9 5.4 | 12.6 54.7 278 17 9 9.9 5.4
9000 12.0 53.6 275 9 5 9.7 5.3 | 13.4 56.1 278 17 9 9.7 5.3
8750 12.7 54.9 276 9 5 9.7 5.3 | 14.1 57.4 278 17 9 9.7 5.3
8500 13.4 56.1 276 9 5 9.7 5.3 | 14.8 58.6 278 17 9 9.7 5.3
8250 14.2 57.6 277 9 5 9.8 5.4 | 15.5 59.9 278 17 9 9.8 5.4
8000 14.9 58.8 277 9 4 9.8 5.4 | 16.3 61.3 278 16 8 10.0 5.5
7750 15.6 60.1 277 8 4 9.8 5.4 | 17.0 62.6 278 16 8 10.0 5.5
7500 16.4 61.5 277 8 4 9.9 5.4 | 17.8 64.0 278 16 8 10.0 5.5
7250 17.1 62.8 278 8 4 10.1 5.5 | 18.5 65.3 278 16 8 10.0 5.5
7000 17.9 64.2 278 8 4 10.2 5.6 | 19.2 66.6 278 16 8 9.9 5.5
6750 18.6 65.5 279 8 4 10.1 5.6 | 20.0 68.0 278 16 8 9.9 5.5
6500 19.4 66.9 279 7 4 10.3 5.6 | 20.7 69.3 279 15 8 10.0 5.5
6250 20.1 68.2 280 7 4 10.5 5.7 | 21.4 70.5 279 15 8 9.9 5.5
6000 20.9 69.6 281 7 4 10.5 5.7 | 22.2 72.0 279 14 7 10.0 5.5
5750 21.7 71.1 281 6 3 10.6 5.8 | 22.9 73.2 279 13 7 9.7 5.3
5500 22.7 72.9 282 6 3 17.1 9.4 | 23.7 74.7 279 12 6 11.4 6.2
________________________________________________________________________________
This product is issued twice per day, once by approximately 0630 MST/0730 MDT
(1330 UTC) and again by approximately 1830 MST/1930 MDT (0130 UTC). It is not
continuously monitored nor updated after its initial issuance.
The information contained herein is based on rawinsonde observation and/or
numerical weather prediction model data taken near the old Stapleton
Airport site in Denver, Colorado at
North Latitude: 39 deg 46 min 5.016 sec
West Longitude: 104 deg 52 min 9.984 sec
Elevation: 5285 feet (1611 meters)
and may not be representative of other areas along the Front Range of the
Colorado Rocky Mountains. Note that some elevations in numerical weather
prediction models differ from actual station elevations, which can lead to
data which appear to be below ground. Erroneous data such as these should
not be used.
The content and format of this report as well as the issuance times are subject
to change without prior notice. Comments and suggestions are welcome and should
be directed to one of the addresses or phone numbers shown at the bottom of this
page. To expedite a response to comments, be sure to mention your interest in
the soaring forecast.
DEFINITIONS:
Convective Condensation Level - The height to which an air parcel possessing the
average saturation mixing ratio in the lowest 4000 feet of the airmass,
if heated sufficiently from below, will rise dry adiabatically until it
just becomes saturated. It estimates the base of cumulus clouds that are
produced by surface heating only.
Convection Temperature (ConvectionT) - The surface temperature required to make
the airmass dry adiabatic up to the given level. It can be considered a
"trigger temperature" for that level.
Freezing Level - The height where the temperature is zero degrees Celsius.
Height of Stable Layer - The height (between 12,000 and 18,000 feet above
mean sea level) where the smallest lapse rate exists. The location and
existence of this feature is important in the generation of mountain
waves.
K Index - A measure of stability which combines the temperature difference
between approximately 5,000 and 18,000 feet above the surface, the amount
of moisture at approximately 5,000 feet above the surface, and a measure
of the dryness at approximately 10,000 feet above the surface. Larger
positive numbers indicate more instability and a greater likelihood of
thunderstorm development. One interpretation of K index values regarding
soaring in the western United States is given in WMO Technical Note 158
and is reproduced in the following table:
below -10 no or weak thermals
-10 to 5 dry thermals or 1/8 cumulus with moderate thermals
5 to 15 good soaring conditions
15 to 20 good soaring conditions with occasional showers
20 to 30 excellent soaring conditions, but increasing
probability of showers and thunderstorms
above 30 more than 60 percent probability of thunderstorms
Lapse Rate - The change with height of the temperature. Negative values indicate
inversions.
Lifted Condensation Level - The height to which an air parcel possessing the
average dew point in the lowest 4000 feet of the airmass and the forecast
maximum temperature must be lifted dry adiabatically to attain saturation.
Lifted Index - The difference between the environmental temperature at a level
approximately 18,000 feet above the surface and the temperature of an air
parcel lifted dry adiabatically from the surface to its lifted condensation
level and then pseudoadiabatically thereafter to this same level. The
parcel`s initial temperature is the forecast maximum temperature and its
dew point is the average dew point in the lowest 4000 feet of the airmass.
Negative values are indicative of instability with positive values showing
stable conditions.
Lift Rate - An experimental estimate of the strength of thermals. It is
computed the same way as the maximum rate of lift but uses the actual
level rather than the maximum height of thermals in the calculation.
Also, none of the empirical adjustments based on cloudiness and K-index
are applied to these calculations.
Maximum Height of Thermals - The height where the dry adiabat through the
forecast maximum temperature intersects the environmental temperature.
Maximum Rate of Lift - An estimate of the maximum strength of thermals. It
is computed from an empirical formula which combines the expected maximum
height of thermals with the difference in the environmental temperatures
between the maximum height of thermals and the temperature 4,000 feet
above the ground. After this computation, further empirical adjustments
are made based on the value of the K-index and the amount and opacity of
middle and high level cloudiness expected between the time of trigger
temperature and the time of overdevelopment.
Middle/High Clouds - The amount and opacity of middle (altostratus, altocumulus)
or high (cirrus, cirrostatus, cirrocumulus) clouds. Broken means that
between 60% and 90% of the sky is covered by the cloud, with overcast
conditions occurring when more than 90% of the sky is covered by the cloud.
Thin implies that the clouds are predominantly transparent, meaning that
some sunlight is reaching the ground, in contrast to opaque which suggests
that little sunlight is reaching the ground.
Potential Height of Wave - The minimum of the following two heights:
1. Level above the height of stable layer (or 14,000 feet if none exists)
where the wind direction changes by 30 degrees or more
2. Level above the height of stable layer (or 14,000 feet if none exists)
where the wind speed no longer increases with height
PVA/NVA - Positive vorticity advection (PVA)/negative vorticity advection (NVA)
on the 500 millibar isobaric surface (approximately 18,000 feet above mean
sea level). Weak PVA has been shown to assist in mountain wave soaring.
Soaring Window - The time between the time the trigger temperature is reached
and the time of overdevelopment.
Thermal Index - The difference between the environmental temperature and the
temperature at a particular level determined by following the dry adiabat
through the forecast maximum temperature up to that level. Negative values
are indicative of thermal lift.
Thermal Soaring Index - An adjective rating (for sailplanes) based on the
computed maximum rate of lift, and the wind speed and middle and high
cloud cover expected during the soaring window (the time of the trigger
temperature and the time of overdevelopment) according to the following:
Maximum rate of lift Adjective Rating
>= 800 fpm Excellent
>= 400 and < 800 fpm Good
>= 200 and < 400 fpm Fair
< 200 fpm Poor
Time of Overdevelopment - The time one or more of the following phenomena,
which essentially shut off thermal lift, is expected to occur:
1. formation of broken to overcast convective cloud cover
2. formation of scattered to numerous downbursts
3. initiation of widespread precipitation
Time of Trigger Temperature - The time the surface temperature is expected to
reach the trigger temperature.
Trigger Temperature - The surface temperature required to make the first 4000
feet of the atmosphere dry adiabatic.
Wave Soaring Index - An empirical, adjective rating (for sailplanes) which
attempts to combine a variety of phenomena important in mountain wave
soaring into a single index number. Objective points are assigned to
these phenomena: wind speed and direction at 14,000 ft MSL, the static
stability in the 12,000-18,000 ft MSL layer, the wind speed gradient above
the stable layer, jet stream location and frontal and upper trough
movements.
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